<!DOCTYPE html>
<html>
<head>
    <meta charset="UTF-8">
    <title></title>
    <style>
        div {
            width: 100px;
            height: 100px;
            background: red;
            opacity: 0.5;
            filter: alpha(opacity=50);
        }
    </style>
</head>
<body>
<!--
    IE8以及IE8以前的浏览器都不支持opacity
    解决办法
        用filter filter:alpha(opacity=50);
-->
<div>kaivon</div>
</body>
</html>
